GRADE GUIDE · MONEL 400
Monel 400 (UNS N04400) is the original nickel-copper alloy — roughly two-thirds nickel, one-third copper — and still the reference material for seawater valve trim, pump shafts and marine fasteners. It is also one of very few metals that handles hydrofluoric acid.
Also listed as: UNS N04400 · EN 2.4360 · NiCu30Fe · Alloy 400
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Monel predates stainless steel and survives because its niche never went away: flowing seawater. Unlike austenitic stainless, it does not pit in chloride crevices, and unlike bronze it keeps real strength — which is why naval hardware, seawater pump internals and desalination fittings still specify it a century on. Its second, narrower fame is chemical: hydrofluoric acid and dry chlorine service, where almost nothing else is safe.
In Gulf yards Monel appears mostly as round bar for shafts and trim, plus sheet for splash-zone sheathing. It work-hardens quickly at the lathe — sharp tools, positive cuts, no dwelling. Surplus bar ends from valve shops are the classic off-cut here, and the nickel content makes even short lengths worth listing; every piece shows its dimensions and weight upfront, and is priced on request.
Crevice and pitting behaviour: 316L pits in stagnant or crevice chloride conditions; Monel resists them and erosion-corrosion in flowing seawater besides. For shafts, trim and fasteners that live wet, Monel is the proven pick.
No — it strengthens only by cold work. Its age-hardenable cousin K-500 (with aluminium and titanium) roughly doubles the strength where a stronger Monel is needed.
Work-hardening. Let a tool rub and the surface hardens ahead of the cut. Rigid setups, sharp inserts, steady feeds — and expect it to feel gummier than stainless.